During El Niño, the tropics emit more carbon dioxide

LOFTY LOOK NASA’s Orbiting Carbon Observatory-2 (shown in an artist’s illustration) launched in 2014 and is giving scientists an unprecedented peek into how carbon moves between land, atmosphere, and oceans on Earth.

The tropics of Asia, Africa and South America all puffed out more carbon dioxide during the strong 2015–2016 El Niño than during the 2011 La Niña, new satellite data show. Because El Niño’s warmer, drier conditions in tropical regions mimic the effects of climate change expected by the end of the century, those observations may be a sobering harbinger of the tropics’ diminishing role as a buffer for fossil fuel emissions (SN Online: 9/28/17).

The new findings come from NASA’s Orbiting Carbon Observatory-2, or OCO-2, which launched in 2014. Five papers in the Oct. 13 Science describe some of the first data collected by the satellite, which is giving scientists an unprecedented peek into how carbon moves between land, atmosphere and oceans.

Gas up

During the 2015 El Niño, tropical regions in three continents released about 2.5 gigatons more carbon (GtC) to the atmosphere than they did in 2011, a cooler and wetter La Niña year (measurement margin of error shown with plus and minus). All three regions saw higher temperatures in 2015 than in 2011, and tropical Asia and South America saw less rainfall, although biomass burning was the primary driver of tropical Asia’s high carbon release.

The cause of those anomalies varied by region, the researchers discovered when they looked more closely at OCO-2 and other satellite data showing changes in biological productivity, carbon dioxide concentration in the atmosphere and other measurements. In Asia, an increase in biomass burning was primarily responsible for the extra carbon release.

But the carbon bumps in Africa and South America were attributable to El Niño, the researchers report: In Africa, higher temperatures drove the larger release of carbon by increasing the rate of plant respiration. In South America, lower precipitation, which reduces the growth of plants, was largely responsible. Both conditions mimic climate changes expected to occur by the end of the century.